Method and arrangement for converting time-modulated pulses into amplitude-modulated pulses



May 23, 1950 G. GUANELLA ETAL 2,508,672

METHOD AND ARRANGEMENT FOR CONVERTING TIME-MODULATED PULsEs INT0 AMPLITUDE-MODULATED PULsEs Filed Aug. '7, 1948 2 Sheets-Sheet l ATTORNEY May 23, 1950 G. GUANELLA ETAL METHOD AND ARRANGEMENT FOR CONVERTING TIME-MODULATED PULSES INTO AMPLITUDE-MODULATED PULSES 2 Sheets-Sheet 2 Filed Aug. 7, 1948 ATTORNEY modulation.

atenteci May 23,

METHOD AND ARRANGEMENT `FOR CN-- VERTING TIME-MODULATED PULSES INTO AMPLITUDE-MODULATED PULSES Gustav vGuanella, Zurich, and Paul Giittinger',V

Wettingen,

Switzerland, assignors to Radio Patents Corporation, New York, N. Y., a corporation of New York Application August 7, 1948, Serial No. 43,144 In Switzerland September 6, 1946 Claims.

(Cl. Z50-27) The present invention relates to pulse modulation, more particularly to a novel method and system for converting time modulated signal pulses into corresponding amplitude modulated -pulses for demodulating or reproducing a signal wave in a receiving station.

- When signals or messages are transmitted by lmeans of time-modulated pulses there is a difierence, according to whether the Width or the position of the pulses is modulated. With widthmodulated pulses, the Width, that is to say the duration of successive pulses, corresponds to the instantaneous values of a modulating signal. With position-modulated pulses, the degree of modulation is characterized by the distance in time of one or both edges of the pulses from equidistant instants. Time-modulated pulses are demodulated by rst converting them into amplitude-modulated pulses. Thereupon, the actual demodulation to the original modulating signal occurs. When converting the width-modulated or position-modulated pulses into amplitudemodulated pulses, it is desirable that the conversion should be as free from distortion as possible.

The present invention is concerned with an improved method and arrangement rfor achieving .this conversion. According to the novel. method,

signal voltage values proportional to the time values characterizing the modulation of the timemodulated pulses are produced, at least part of isaid signal voltage values being stored, in such a manner as to result in pulses which occur at equal intervals and have an amplitude proportional to said voltage values.

Further objects and novel aspects of the invention Will become more apparent from the following detailed description taken in reference to the accompanying drawings forming part of this l specification, and wherein:

Figures l, 2, 3a to 3d and 5a to 5d are theoretical diagrams explanatory ofthe function and operation of the invention; and

Figures 4 and 5 are wiring diagrams of suitable circuit arrangements for carrying out the invention.

Referring to Figure 1, J1, J2, J3 etc. are timemodulated pulses shown for different degrees of The instants at which the ypulses commence are characterized by the position of the left-hand pulse edges and follow each other at equal intervals of time T. The durations X1, X2, X3 etc. of the pulses are the momentary time values which characterize the degree of modulation or instantaneous modulating signal Values and serve to produce the time-proportional Volt-f age values Y1, Y2, Ya. These voltage values attain their values Y1, Y2; Ya at the end of each pulse,

such lasv by charging a condenser with constant current during a time corresponding to the pulse durations X1, X2, X3.

' There are obtained in this manner amplitude modulated pulses Z1, Z2, Z3 corresponding to the voltages Y1, Y2, Ys. Ii these amplitude modulated pulses occured immediately at the end of the vpulses (right-hand pulse edge), as would be the simplest arrangement, they would not be spaced by equal intervals. This would result in nonlinear distortion at the output of the demodulater. According to the invention this distortion is avoided by making the amplitude-modulated pulses follow each other at equal intervals T=T. This is achieved by storing the voltage values Y1, Y2,.Ys and only allowing them to become effective at equidistant points in the form of the amplitude-modulated pulses Z1, Z2, Z3. S1, S2, S3 indicate the corresponding storage times. Thus, the amplitude-modulated pulse occurs only towards the end oi an interval T. It is also possible to `allow the pulse Z1 to occur` at the instant P1 when the next pulse X2 begins, since the pulses start at equal intervals. In all events, the amplitude-modulated pulses Z succeed each other at equal intervals T, that is at equidistant time positions, so that the demodulation will be linear and accurately follows the shape or curve of the original modulating voltage.

Anotherv use of the method according to the invention relates to the demodulation of widthrnodulated pulses of the type shown in Figure 2. Here, the pulses are modulated in such a manner that `the distance in time of both edges of the puises from equidistant points P111, P111, Ps2, P112, Pas, Phs etc. serves as the time value characteristic of the instantaneous modulating signal values. Thus, the equidistant instants of time occur at 'double the pulse frequency, so that every second `At the instant when the pulse stops, the voltage vYb1 has also reached its end value.

The pulse proportional to this voltage should not, however,

occur at this instant, but somewhat later 'at the instant P111. According to the invention, the voltage Ybi is therefore stored during the time S1.

The same process repeats itself With all the subsequent pulses. The modulation pulses Zal, Zbl, Zaz, Z112 etc., occur thus at equal intervals, Whereby to fuliill an important condition -ior a distortion free demodulation accordingly, the ,envelope U corresponds to the'modulation curve orsignjal at the transmitter. This applies particularly to transmission where the time-modulated pulses at the transmitter are also obtained from equidistant modulating values Zin, Zm etc., asshow'nAVV and described in our U. S. Patent No. :2,435,496,- entitled Impulse modulation system.

As soon as the terminal b tends to become positive, a current flows through the rectifier, which prevents a voltage rise in the opposite direction. This charging and discharging process is illus- Ltratedhin*.Fi gure 3c. .Charging-.fis'ornpleted at vthe points Pai, Ps2 etc. The charging voltage Uabi, Um etc. corresponds to the prevailing duration of the pulses shown in Figure 3b, and furthermore-corresponds to the time values ai, d2, a3 etc. of Figure 2. The actual amplitudemodulated pulses which occur at equidistant time As will be understood, the. method according.,toy the invention may be applied. to. otherdiinds ofy time-modulated pulses, for instance` positionmodulated pulses.

The arrangement for carryingout the `method according to the invention will now be explained with reference to width-modulated pulses of the kind shown in Figure 2. The arrangementin- ,proportional to the voltage values Yai, Yin, Yau,

Ybzletc. The conversion takes lplace in two sepa.- rate operations, whereby the timevalue for the left-.hand-edge, that is, at the beginning of the pulse, and the time value for the right-hand edge at the end of the pulse cause control systems to operate alternately.

The conversion of the time values of the lefthandpulse edges with reference .to vtheequidistant points Pai, Paz, Paz will be .explained-by reference to the diagrams .of Figures 3a to.3 d and the. circuit arrangement-shown. in Figure 4.

The width-modulated pulses of amplitudeUo, Figure 3a, received from the transmitter are applied'to the control .grid oi a tubeVL together with a pulse voltage U1 obtained froma Vsuitable generator operated in synchronism with the received pulses. The local pulses U1 have 1a phase lead of 90- relativeto the Areceived pulses ,Uo. Thetwo..pulses .applied to the) control grid are shown in Figure 3a. The .grid bias 4voltage of tube V1. is so selected that the Working. pOIlt-is at thelower bend of thetube operating,..char acteristic. An anode current will therefore only :dow.when both grid voltages, arepositive. Timemodulated .pulses such as indicated .by the shaded areas Uo-i-Ui `in Figure 3b will thus occurin the anode .circuit of the tube. `The width of these pulses corresponds to the time values a1, az, aa, etc..of Figure 2. As soon as the voltagek Uo-l-Ui is positive` and exceeds a certain. value'S, an anodev current JL flows through the tube VL, charging the condenser C negatively at the terminalb through .a resistance R. VOwirigto the Avoltage drop .across the resistance R. the tube .VE :will remain blocked until the current I1. ceases A to flow. This is the case at the equidistancenpoints P81, Paz, PasV etc. After thisV instant the ltube VE allows current to pass again, owing toits A grid.` being positive. AAs Va res.ult,ithe\condenser C is discharged by a discharging current JE ilowing through the tube VE. The condensershould however only discharge until reaching zerovoltage. In .order to achieve lthis and to ,prevent positionsare produced by means of a further tube V11.` To :this end, part of the condenser voltage is A:applied.througha potential-divider R1, R2, to thegrid-of--tubeVa Normally while a pulse is receivedythetube is blocked. The grid of tube Varurther'more has applied to it equally spaced shortpu'lses U2, Figure 3d, through a resistance Rga. The amplitude of these pulses is so selected as to just reach the starting point of the anode current. 'The proportionall partsv of the condenser voltages Um, Uabz. ete. are thusadded' 'to thepulsevoltages Uafso thatthe anode currents pulses of tube Varareproportional to:the;.con-

.denser voltages and in turn `tothe time .values a1, a2, a3 etc.

The conversion of the-time values of the Arighthand pulse edges-.with reference to theequidis'- tant :points-.is illustratedin Figures...5 'and'.. For .thepulses shown. in:Fig-ure.-2, these time `values are lan-bz, b3 .etc. Y These .valueshavefto'fbe converted. into .proportional :voltage values Yci, Ycaetc. andnstored during the -periodssmA S2,--'ete. in order toproduce proportional-irnpulseszzen 35 Zbaetc.. atlthe.equidistant-points- Pm; Pbzfas shown in Figure 2.

A circuit arrangement `'for convertingv thetim'e values of .theright-hand-pulse edges is shown in-Figure 6.

Inthe latter,W the `input lgridof Vtube-'Vrin 'excitedl bythe width-modulatedpulses 'U0 Ireceived from the transmitter anda pulse voltage V1 supplied 'by a-local generaton The local pulses have a phase lag-of 90911relative to the received pulses. The pulses on the control grid of tube V1. are shown in Figure-5a. The grid bias volt- `ageis again so vselected that the working-point lies v*on-the lower bend of the characteristicfoperating curve of the tube.'-,Ananode current thus flows only whenboth'the grid control voltages are positive. Thus time-modulated -pulseshocour in -the anode circuit, such--asare indicated by the shaded areas4 in -Figure 5b.; AThe width of these pulses corresponds to thewtimef values-b1, b2, bis, etc. of Figure 2. As soon asthe voltage Uo-l-U1 becomes positive, an anode current Jr. flows in 4the tube VL', ywhich charges the -condenserl C' negatively at the4 terminal b.V The charging voltage Vas attainedafter eachpulse is proportional to theiduration of `the shaded pulses* shown Figure 5b;YV At theend'of the pulses, voltages Vahr, Vasa, etc. onthe condenser C remain ystored fonthe periods Si, 'S2 etc. up to the instants Phi, -Pbzj'etd These instants lie in the middle between the equidistant Pai, Paz, Pas. ,At the instar1-ts,PhiJ P bz, Pbziietd pulses. with. on .amplitude proportional V'to 'the stored `voltages Vasi, Vabz etc,v areproduced. -This is achieved by Aremlering ua `parallel=connectei tube VEZ current-,conductive,` at the linstants Ps1, Pb2etc...byapplying-the, pulsefvoltage V1 'to the screen .grid SG.t thereof., .The .screen grid is c onnected through Va choke. boil-.13. withftheanode-A. The-.oondensordisoharsosthtoushthe tube down to zoravolteeosg-A rectifier- Git is connectedin iiiiiggui pulses at theiiistanisfrsifisiaed .e inruief'tube vs' Paiste; isfsprevidea fra ed -inpaiaueiwithitneciiensr control grid also has control ypiilssfVz (Figure d) applied to it through a r'sistancftlis pulses 1 producing corresponding *anode curi-ent pls'sli'; The contlpu1ss V a'i'dth Iii oltesare so selected thatftlie fctrp tion of" the condenser voltage: produces proportional current pulses. Y

'Ilie'i' iving arrangement combines the two arra'gftssliwi ifFigures 4 and 6. At the output end of this combinedy receiving larrangement there are obtained amplitude-modulated pulses according to Figurescand- 5c. The-pulses follow each other at constant intervals-Pan Pi, Ps2, Pez etc. with twice as many pulses as there are width-modulated pulses atV the input end of thek'ar'raingement. The pulse l voltage U9 sug'plid both' arrangements may for irristan'cel' be" 'divedfrom a commonreceiver'inwhichtlielighfrequency pulse signals received through an aerial are amplied and converted into width-mode ulated pulses. Operating in synchronism with ther electron discharge device contrllid'bythe received signal pulses is =a generator producpulses also in synchronism with the pulse repeing the non-modulated control pulses U1 and V1 30 tition frequency, said last device being connected for both systems. The generator is provided with to said condenser to derive successive amplitude special means, whereby the pulses supplied to modulated discharge current pulses of constant both amplifiers are phase-displaced by 90 comwidth spaced by equal time intervals from each pared with the non-modulated receiving pulses. other. Voltage U1 leads the voltage U0 and voltage V1 35 4. In a method of receiving signal pulses havlags behind the voltage Uu. ing equi-spaced starting edges and Widths modu- The output ends of the amplifiers are conlated according to the instantaneous values of a nected in parallel so that there is double the modulating signal, the steps of converting said number of pulses in the common output circuit. signal pulses into pulses of constant width and The pulses succeed each other at constant in- 40 amplitude proportional with the respective tervals of time, and have their amplitude moduwidths of the original pulses, and variably delaylated in accordance with the time values of the ing the converted pulses to produce substantially width-modulated pulses. equi-spaced final pulses having amplitudes vary- When time-modulated pulses of the kind ing according to said modulating signal. shown in Figure l have to be converted into am- 5. In a method of receiving modulated signal plitude-modulated pulses, the arrangement pulses of constant amplitude and having equishown in Figure 6 can be used. In this case it spaced starting edges and widths proportional to is also necessary to store the voltages Y1, Y2, Ya, the instantaneous values of la modulating signal, etc. during the corresponding times Si, S2, S3, etc. the steps of converting the received pulses into We claim: pulses of constant width and amplitude varying 1. In a system for receiving width modulated in proportion to the widths of the respective origsignal pulses of the type having equi-spaced inal pulses, and variably time delaying' the constarting edges and widths proportional to the inverted pulses to produce substantially equistantaneous values of a modulating signal, =a conspaced nal pulses having amplitudes-varying in denser with means for successively charging the accordance with said modulating signal. same by the received signal current pulses, rst 6. In a method of receiving width modulated Switching means operated in Synchronism with signal pulses of constant amplitude and having the pulse repetition frequency to initiate a disequi-spaced starting edges and widths proporcharge of said condenser after lapse 0f predeteltional to the instantaneous amplitudes of a modmined equal ilim@ interi/31S from each Starting ulating signal, the steps of integrating the reinstant of SuCCeSSiVe Signal DUISS. and fuihe ceived signal current pulses to produce voltages Switchlng means 211'S0 Operated 11'1 Synchomsm having amplitudes proportional to the respective with the pulse repellOD frequency and com leci'- pulse widths, and vari-ably storing said voltages ed to said condenser for segregating amplitude and deriving equi spaced Signal pulses of conmodulated discharge current pulses of constant 'si-,ant Width from t to l Width spaced from each other by equal time in- 05 he s red v0 tages havmg am tervals p litudes varying according to said modulating 2. In a system :for receiving width modulated slnallll t f l signal pulses of constant amplitude and having af sys em or I 'ecelvmg slgnal pulses hav' equi-spaced starting edges and widths propormg eqll'spad Startnfg edgesand Wl'dths mod' tional to the instantaneous values of a modulat- 1?'ted m accordance Wlth 12h@ lnsta'ntaneous a'm ing signal being received, an input circuit, a conplltlides 0f a modulatmg signal, means for intedenser, a constant current device connected begmtmg the reCeWed pulses '00 Produce voltages tween said input circuit to said condenser to having amplitudes Varying in proportion to the successively charge said condenser by the signal respective pulse widths, means for variably time current pulses to voltages proportional to the u delaying the integrated voltages and deriving therefrom ilnal voltage pulsesl of constant width atequidistant spacing intervals equal to the original pulse spacing intervals.

8. In a system for receiving Width modulated signal pulses of constant amplitude and having `equi-spaced starting edges and Widths proporf tional to the instantaneous amplitudes of a modulating signal, means for integrating the re ceived signal pulses to produce voltages having amplitudes proportional to the respective pulse Widths, means for variably storing said voltages and for deriving therefrom iinal substantially equi-spaced voltage pulses of substantially constant width and having amplitudes Varying in accordance with said modulating signal.

9. In a method of receiving width modulated signal Apulses of constant amplitude having equispaced starting edges and widths proportional to the instantaneous amplitudes ofa modulating signal, the steps of integrating the received signal pulses to produce voltages having amplitudes proportional tothe respective pulse widths, and variably storing said voltages and deriving therefrom final equi-spaced Voltage pulses of constant width and having a frequency equal to the original pulse repetition frequency and having amplitudes varying in accordance with said modulating signal, Y y

tional to the respective pulse Widths, means for '.variably storing said voltages and for deriving therefrom Vinal substantially equidistant pulses otjconstant width, said final pulses having a frequency equal to the original pulse repetition frequency and amplitudes varying in accordance With the instantaneous amplitudes of said modulating signal.

GUSTAV GUANELLA.

PAUL GTTINGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS vNumber Name Date 2,438,907 Frankel et al. Apr. 6, 1948 2,457,140 Frankel Dec. 28, 1948 

